The construction of insulating glass units comprising two-pane or multi-pane glass is known. In addition to the glass panes, it is standard practice to use sealants and/or adhesives, spacers and desiccants or water scavengers for this purpose. Solar-module glazing (both photovoltaic solar modules and solar modules for heating water) is assembled in the same way, except that the two glass panes can be replaced partially or completely by sheet metal and/or plastic film.
The spacer consists primarily of metal (usually aluminum), is located in the edge area of the glass panes, and has the function of maintaining the two glass panes at the desired distance apart. A desiccant (e.g. a molecular sieve) is contained additionally within the hollow spacer in order to keep the air or gas trapped between the panes dry. To enable the desiccant to absorb moisture at all, the spacer is provided with small apertures (longitudinal perforation) on the side facing the interpane space. This arrangement prevents moisture from condensing on the inside of the glass panes at low ambient temperatures and impairing the transparency of the insulating glass unit.
Between the sides of the spacer that face the glass panes and the inner surfaces of the glass panes, a seal based on polyisobutylene and/or butyl rubber is provided. This seal is generally known as the primary seal. The function of the primary seal is during production of the insulating glass panes, to be a kind of “assembly aid” while the glass panes are being joined to the spacer, which has been pre-coated with primary sealant, in order to hold the assembly together during the next production stages, and later, during the service life of the insulating glass unit, to form a water-vapor barrier that prevents moisture from penetrating from the exterior inwards into the interpane space, and, if the insulating glass unit is filled with gas, to prevent loss of this gas outwards from the interpane space.
As the outward-facing edge of the spacer is a few millimeters inside of the outside edges of the glass panes, a “channel” is formed into which the secondary sealant, as it is generally known, is injected. The main purpose of the secondary seal is to elastically bond the edge of the insulating glass unit (glass panes and spacer) and also to form a seal—which is to some extent an additional seal—against water and water vapor from the outside and gas from the inside (interpane space). As a rule, the secondary seal consists of room-temperature-curing, two-part sealants and/or adhesives based on polysulfide, polyurethane or silicone. One-part systems, for example based on silicone, or a hot-melt butyl adhesive applied while hot, are also possible.
The systems described above, however, also have certain disadvantages. During production of the insulating glass units, a large number of materials have to be processed in a series of complicated and cost-intensive stages, some of which take place simultaneously.
As far as the thermal insulation properties of the edge seal are concerned, metal spacers used there have the disadvantage of being good heat conductors and thus having a negative influence on an insulating glass pane's desirable low K-value, which, in the case of double- or multi-pane insulating glass, has been improved substantially in recent years by filling the interpane space with inert gas and using glass panes coated with low-emission (low-E) layers.
Particularly as a consequence of the second disadvantage, increasing numbers of insulating glass systems have become available recently which, in place of aluminum as spacer, use: prefabricated stainless steel profiles (lower wall thickness possible and hence reduced heat flow); or prefabricated plastic profiles; or prefabricated thermoplastic profiles; or extrusion compound comprising thermoplastic materials extruded directly onto one of the glass panes. On account of the improved thermal insulation properties in the edge seal, these systems are also known as “warm-edge systems”. Examples of the above may be found in EP 517 067 A2, examples and application machinery for in EP 714 964 A1, EP 176 388 A1 and EP 823 531 A2.
The DE 196 24 236 A1 describes a hot-melt adhesive composition for insulating glass, containing a mixture of at least one reactive binder based on silane-functional polyisobutylene, hydrogenated polybutadiene and/or poly-α-olefins, and a non-reactive binder from the group comprising the butyl rubbers, poly-α-olefins, diene polymers, polybutene or styrene block copolymers, which composition may be used as 1- or 2-part adhesive/sealant in the production of insulating glasses. No separate spacers comprising metal or plastic profiles are needed here, and no additional, secondary sealants.
The DE 198 21 355 A1 describes a sealing compound for use in the production of multi-pane insulating glass; the compound contains silane-modified butyl rubber and serves as spacer between the individual panes of the multi-pane insulating glass. Here too, no secondary sealant is needed.
Particularly those spacers extruded directly onto one of the glass panes also overcome the problems relating to the manufacturing process. As a result, insulating glass panes can be made using an automated process which is much more flexible and more productive.
In the field of solar module manufacture, too, applying the spacer directly onto the module edges in this manner has proved to offer many advantages. Compared, for example, with the manual or semi-automatic fitting of pre-extruded butyl tapes, this solution brings not only optical advantages but also productivity advantages; in addition, it makes for a more reliable long-term barrier against water-vapor penetration and gas leakage. The EP 1 615 272 A1 (or DE 10 2004 032 604 A1) contains a description of an exemplary method and device for assembling solar modules.
The thermoplastic material used combines the function of the spacer with that of the primary seal, as it is called. It also contains the desiccant. The TPS system (TPS=thermoplastic spacer) is an example of such a system.
With these systems, too, the outward-facing edge of the spacer is a few millimeters inside of the outer edges of the glass panes, and the remaining space is filled by the secondary seal, as it is called, which bonds the units elastically.
Where silicone is used as the secondary sealant in combination with a thermoplastic spacer such as the TPS system, it has been found that insulating glass units, including those filled with inert gas, can be manufactured substantially more reliably and retain their gastightness in the edge seal even after a large number of weathering cycles (EP 916 801 A2). It is very difficult to obtain equally low gas-leakage rates when using metallic spacers combined with a standard primary seal and a silicone-based secondary seal.
Combined with polysulfide as secondary sealant, the TPS system has, over the past ten years, proved to be completely unproblematic in insulating-glass fenestration applications.
However, particularly in cases where silicone is used as a secondary sealant, there is a disadvantage that can, in certain cases, manifest itself as an optical defect within the insulating glass units. A combination of:    a) materials (e.g. weather seal, EPDM glazing profiles, etc.) which, due to external influences, are not compatible with the insulating-glass edge seal, and    b) construction errors in the glazing area of the insulating glass units, caused by inadequate planning (poor ventilation/drainage of the glass rebate), and    c) extreme exposure (particularly high temperatures at the insulating glass pane and in the edge seal) due to the situation of the installation can cause deformation or movement of the thermoplastic spacer profile into the interpane space. This phenomenon is also known in German as the “Girlanden-Effekt”. Depending on the quality of the TPS sealant used, (formulation/production process), there are marked differences in susceptibility to the external influences described under points a) to c). Where silicone is used as secondary sealant, the main reason may be assumed to be the lack of adhesion between the TPS sealant and the secondary seal, and the inadequate adhesion—based only on predominantly physical interactions—of the TPS sealant to the glass. This bond may be easily weakened to a greater or lesser extent by substances migrating into the glass/TPS sealant interface.
Proposals for creating a connection of such kind between the TPS and the silicone secondary seal as to achieve mechanical anchorage or a frictional connection by way of a specially shaped cross-section for the extruded TPS profile (DE 102 04 174 A1) unfortunately cannot be implemented due to the impossibility of obtaining a suitably shaped die for extruding such a profile cross-section. Another problem with this proposal that has not been solved is exactly how to join up the beginning and the end of the spacer profile extruded onto the glass pane. For a normal rectangular cross-section, this has been described and solved in the EP 823 531 A2. A further difficulty with this proposal is encountered while applying the secondary sealant and consists in how to completely fill the partially convex voids within the TPS strand without incorporating any air bubbles. All in all, therefore, this proposal is one that cannot be implemented as such in an everyday production process, and accordingly does not establish the desired objective.
Attempts to achieve chemical adhesion between the TPS sealant and the silicone sealant by selective addition of traditional, silane-based adhesion promoters to one and/or both sealants also fail. To this end, it is desirable to use grades and quantities which unfortunately have a negative influence on other desired properties, for example the working consistency of the TPS sealant, or which later on cause fogging in the insulating glass when the unit has been installed.